An amateur is someone who is doing it (whatever "it" is) without being paid by someone a fee to do it. An amateur investor is someone who is investing their ow

An amateur is someone who is doing it (whatever "it" is) without being paid by someone a fee to do it. An amateur investor is someone who is investing their own money. A professional investor is an investor who is being paid by somebody else (a fee of some kind) to do the investing on their behalf. Amateur/professional doesn't refer to the method they invest using. They could be using gold-fish to tell them what to buy, or they could be using sophisticated computer and math models to buy/sell.